Underground cribbing is commonly used in mines for supporting a mine roof or the like. The cribbing is formed of cribbing elements such as wooden beams or concrete blocks, which are stacked from the mine floor to the mine roof in order to provide support for the roof.
Although many different types of cribbing elements have been proposed for the support of mine roofs, they are typically assembled in a similar manner in the mine. Typically, the cribbing elements are much smaller in height than the distance between the mine floor and the mine roof, and therefore a great many cribbing elements must be transported to the mines and then assembled at each location in which the roof needs to be supported.
Assembling the separate cribbing elements into a mine support is typically laborious and requires a significant amount of time. When stacked vertically, some common cribbing elements must have their outer perimeters in alignment. Other types include notches or other features that require interlocking of adjacent elements to keep them in alignment. Since the cribbing elements are typically much less in height than the clearance between the floor and roof, a significant amount of time and effort are expended at each separate roof support location.
An additional problem arises with cribbing elements constructed of concrete blocks. Typically, mine floors are not perfectly level. They may have slight slopes or may have uneven surfaces. This typically doesn't present a problem when the cribbing elements are constructed of an easily compressible material such as wood, as the wood elements will deform in the area of the high spot on the uneven surface. However, when using concrete block cribbing elements, the relatively uncompressible blocks may break on a high spot on the uneven surface.
Another problem arises with cribbing elements that are aligned along their outer peripheries. Since a large number of cribbing elements must be aligned laterally while building the vertical support, it is sometimes difficult to obtain a true lateral alignment of the elements. If one or more of the cribbing elements is out of lateral alignment, the entire surface of the misaligned cribbing element is not available to support the load, thereby increasing the specific loading per area on the cribbing element and possibly leading to premature failure of the roof support.
Therefore, as should be obvious by the above description, prior art mine roof supports constructed of separate cribbing elements can be improved.